1 /* 2 * Copyright (C) 1984-2020 Mark Nudelman 3 * 4 * You may distribute under the terms of either the GNU General Public 5 * License or the Less License, as specified in the README file. 6 * 7 * For more information, see the README file. 8 */ 9 10 11 /* 12 * Routines dealing with the "position" table. 13 * This is a table which tells the position (in the input file) of the 14 * first char on each currently displayed line. 15 * 16 * {{ The position table is scrolled by moving all the entries. 17 * Would be better to have a circular table 18 * and just change a couple of pointers. }} 19 */ 20 21 #include "less.h" 22 #include "position.h" 23 24 static POSITION *table = NULL; /* The position table */ 25 static int table_size = 0; 26 27 extern int sc_width, sc_height; 28 29 /* 30 * Return the starting file position of a line displayed on the screen. 31 * The line may be specified as a line number relative to the top 32 * of the screen, but is usually one of these special cases: 33 * the top (first) line on the screen 34 * the second line on the screen 35 * the bottom line on the screen 36 * the line after the bottom line on the screen 37 */ 38 public POSITION 39 position(sindex) 40 int sindex; 41 { 42 switch (sindex) 43 { 44 case BOTTOM: 45 sindex = sc_height - 2; 46 break; 47 case BOTTOM_PLUS_ONE: 48 sindex = sc_height - 1; 49 break; 50 case MIDDLE: 51 sindex = (sc_height - 1) / 2; 52 break; 53 } 54 return (table[sindex]); 55 } 56 57 /* 58 * Add a new file position to the bottom of the position table. 59 */ 60 public void 61 add_forw_pos(pos) 62 POSITION pos; 63 { 64 int i; 65 66 /* 67 * Scroll the position table up. 68 */ 69 for (i = 1; i < sc_height; i++) 70 table[i-1] = table[i]; 71 table[sc_height - 1] = pos; 72 } 73 74 /* 75 * Add a new file position to the top of the position table. 76 */ 77 public void 78 add_back_pos(pos) 79 POSITION pos; 80 { 81 int i; 82 83 /* 84 * Scroll the position table down. 85 */ 86 for (i = sc_height - 1; i > 0; i--) 87 table[i] = table[i-1]; 88 table[0] = pos; 89 } 90 91 /* 92 * Initialize the position table, done whenever we clear the screen. 93 */ 94 public void 95 pos_clear(VOID_PARAM) 96 { 97 int i; 98 99 for (i = 0; i < sc_height; i++) 100 table[i] = NULL_POSITION; 101 } 102 103 /* 104 * Allocate or reallocate the position table. 105 */ 106 public void 107 pos_init(VOID_PARAM) 108 { 109 struct scrpos scrpos; 110 111 if (sc_height <= table_size) 112 return; 113 /* 114 * If we already have a table, remember the first line in it 115 * before we free it, so we can copy that line to the new table. 116 */ 117 if (table != NULL) 118 { 119 get_scrpos(&scrpos, TOP); 120 free((char*)table); 121 } else 122 scrpos.pos = NULL_POSITION; 123 table = (POSITION *) ecalloc(sc_height, sizeof(POSITION)); 124 table_size = sc_height; 125 pos_clear(); 126 if (scrpos.pos != NULL_POSITION) 127 table[scrpos.ln-1] = scrpos.pos; 128 } 129 130 /* 131 * See if the byte at a specified position is currently on the screen. 132 * Check the position table to see if the position falls within its range. 133 * Return the position table entry if found, -1 if not. 134 */ 135 public int 136 onscreen(pos) 137 POSITION pos; 138 { 139 int i; 140 141 if (pos < table[0]) 142 return (-1); 143 for (i = 1; i < sc_height; i++) 144 if (pos < table[i]) 145 return (i-1); 146 return (-1); 147 } 148 149 /* 150 * See if the entire screen is empty. 151 */ 152 public int 153 empty_screen(VOID_PARAM) 154 { 155 return (empty_lines(0, sc_height-1)); 156 } 157 158 public int 159 empty_lines(s, e) 160 int s; 161 int e; 162 { 163 int i; 164 165 for (i = s; i <= e; i++) 166 if (table[i] != NULL_POSITION && table[i] != 0) 167 return (0); 168 return (1); 169 } 170 171 /* 172 * Get the current screen position. 173 * The screen position consists of both a file position and 174 * a screen line number where the file position is placed on the screen. 175 * Normally the screen line number is 0, but if we are positioned 176 * such that the top few lines are empty, we may have to set 177 * the screen line to a number > 0. 178 */ 179 public void 180 get_scrpos(scrpos, where) 181 struct scrpos *scrpos; 182 int where; 183 { 184 int i; 185 int dir; 186 int last; 187 188 switch (where) 189 { 190 case TOP: 191 i = 0; dir = +1; last = sc_height-2; 192 break; 193 case BOTTOM: case BOTTOM_PLUS_ONE: 194 i = sc_height-2; dir = -1; last = 0; 195 break; 196 default: 197 i = where; 198 if (table[i] == NULL_POSITION) { 199 scrpos->pos = NULL_POSITION; 200 return; 201 } 202 /* Values of dir and last don't matter after this. */ 203 break; 204 } 205 206 /* 207 * Find the first line on the screen which has something on it, 208 * and return the screen line number and the file position. 209 */ 210 for (;; i += dir) 211 { 212 if (table[i] != NULL_POSITION) 213 { 214 scrpos->ln = i+1; 215 scrpos->pos = table[i]; 216 return; 217 } 218 if (i == last) break; 219 } 220 /* 221 * The screen is empty. 222 */ 223 scrpos->pos = NULL_POSITION; 224 } 225 226 /* 227 * Adjust a screen line number to be a simple positive integer 228 * in the range { 0 .. sc_height-2 }. 229 * (The bottom line, sc_height-1, is reserved for prompts, etc.) 230 * The given "sline" may be in the range { 1 .. sc_height-1 } 231 * to refer to lines relative to the top of the screen (starting from 1), 232 * or it may be in { -1 .. -(sc_height-1) } to refer to lines 233 * relative to the bottom of the screen. 234 */ 235 public int 236 sindex_from_sline(sline) 237 int sline; 238 { 239 /* 240 * Negative screen line number means 241 * relative to the bottom of the screen. 242 */ 243 if (sline < 0) 244 sline += sc_height; 245 /* 246 * Can't be less than 1 or greater than sc_height. 247 */ 248 if (sline <= 0) 249 sline = 1; 250 if (sline > sc_height) 251 sline = sc_height; 252 /* 253 * Return zero-based line number, not one-based. 254 */ 255 return (sline-1); 256 } 257